New Zealand city commissions MBR wastewater upgrade

The city of Rotorua on New Zealand’s North Island has become the first city in the country to use a membrane bioreactor (MBR) for wastewater treatment on a major scale.

The city was also the nation’s first to use the five-stage Bardenpho biological treatment process.

Rotorua District Council (RDC) announced on 12 July 2012 completion of an NZ$ 8.5 million (US$ 6.7 million) upgrade of its 20,000 m³/d wastewater treatment plant which includes the commissioning of new MBR technology to further improve Rotorua’s lake water quality.

“With membrane filtration technology we’re able to remove very minute particles containing nitrogen and phosphorus, on top of the already successful biological removal process,” said RDC utilities operations manager Eric Cawte. “About a third of the sewage is treated in this way, enabling the current process to operate to its maximum efficiency without flow fluctuations.”

“It also provides us with additional capacity for treating extra sewage now being transferred from a number of lakeside communities, and which would otherwise be at risk of leaching nutrients into our lakes from septic tanks,” he added.

Cawte said the city’s wastewater plant had historically treated sewage effectively and produced very high quality effluent which was in turn used for irrigating parts of the Whakarewarewa Forest. However achieving the desired limits for nutrient nitrogen entering Lake Rotorua via the Puarenga Stream had always been challenging due to a number of natural factors.

The district council was now in the process of preparing an application to the Bay of Plenty Regional Council to amend resource consent conditions. It would be acknowledgement of the new high level of treatment being achieved at the waste water treatment plant.